This invention relates to a semiconductor wafer dividing method for dividing a semiconductor wafer, in which a plurality of rectangular regions are demarcated by streets arranged in a lattice pattern on the face of the semiconductor wafer, and a semiconductor circuit is disposed in each of the rectangular regions, into the individual rectangular regions.
For production of a semiconductor chip, as is well known among people skilled in the art, it is common practice to demarcate a plurality of rectangular regions by streets arranged in a lattice pattern on the face of a semiconductor wafer to form a semiconductor circuit in each of the rectangular regions. The thickness of the semiconductor wafer is sufficiently decreased, and the semiconductor wafer is divided into the individual rectangular regions, whereby semiconductor chips are produced. A customary mode of decreasing the thickness of a semiconductor wafer and dividing the semiconductor wafer into the individual rectangular regions comprises grinding the back of the semiconductor wafer to impart a required thickness to the semiconductor wafer, and then cutting the semiconductor wafer along the streets to form the individual rectangular regions. Instead of this customary mode, a mode, called dicing-before-grinding, has recently been proposed and put to practical use. According to the dicing-before-grinding mode, a semiconductor wafer is cut along streets to a predetermined depth, rather than over the full thickness of the semiconductor wafer, to form grooves along the streets on the face of the semiconductor wafer, and then the back of the semiconductor wafer is ground to make the thickness of the semiconductor wafer not more than the depth of the grooves, for example, about 50 xcexc, thereby dividing the semiconductor wafer into individual rectangular regions. Grinding of the back of the semiconductor wafer is carried out by rough grinding at a relatively high speed with the use of rough grinding means containing relatively large diamond grains, followed by precision grinding at a relatively low speed with the use of precision grinding means containing relatively small diamond grains. From the point of view of the grinding efficiency, it is desired that the thickness ground by rough grinding be maximized, while the thickness ground by precision grinding be made a minimum required value.
The aforementioned conventional semiconductor wafer dividing method, called dicing-before-grinding, poses the following problems to be solved: The depth of the grooves formed on the face of the semiconductor wafer tends to fluctuate, although slightly, owing to abrasion of the cutting means caused by repeated cutting, and fluctuations in ambient temperature at which cutting is performed. Because of the fluctuations in the depth of the grooves, even when the semiconductor wafer is brought to a predetermined thickness by grinding the back of the semiconductor wafer, there may be cases in which the depth of the grooves is smaller than the thickness of the semiconductor wafer, accordingly, the rectangular regions are not divided individually. Alternatively, while the back of the semiconductor wafer is being ground roughly, the thickness of the semiconductor wafer may become not more than the depth of the grooves, with the result that the rectangular regions may be divided individually before precision grinding is performed. If the. semiconductor wafer is divided into the individual rectangular regions prior to precision grinding, the rough grinding means acts on the edges of the individual rectangular regions, i.e., semiconductor chips, so that intolerable chipping often occurs in the edges of the semiconductor chips. Furthermore, the back of the semiconductor chips is not sufficiently smooth.
A principal object of the present invention is to improve the semiconductor wafer dividing method, called dicing-before-grinding, thereby making it possible to divide a semiconductor wafer into individual rectangular regions sufficiently satisfactorily, without posing intolerable problems, even if the depth of grooves formed on the face of the semiconductor wafer slightly fluctuates.
The inventors of the present invention conducted in-depth studies, and have found that the above-mentioned principal object can be attained by measuring the depth of grooves formed on the face of a semiconductor wafer before grinding the back of the semiconductor wafer, for example, whenever a predetermined number of the semiconductor wafers are to be divided, and then controlling rough grinding and precision grinding during the grinding step in accordance with the depth of the grooves measured.
According to the present invention, there is provided, as a semiconductor wafer dividing method which attains the aforementioned principal object, a semiconductor wafer dividing method for dividing a semiconductor wafer, in which a plurality of rectangular regions are demarcated by streets arranged in a lattice pattern on the face of the semiconductor wafer, and a semiconductor wafer is disposed in each of the rectangular regions, into the individual rectangular regions, comprising:
a groove cutting step of cutting the face of the semiconductor wafer along the streets to form grooves along the streets on the surface of the semiconductor wafer; and
a back grinding step of grinding the back of the semiconductor wafer to reduce the thickness of the semiconductor wafer to not more than the depth of the grooves, thereby dividing the semiconductor wafer along the streets, and wherein:
a groove depth measuring step of measuring the depth of the grooves is incorporated before the back grinding step; and
in the back grinding step, rough grinding is performed until the thickness of the semiconductor wafer becomes greater than the depth of the grooves by a predetermined value, and then precision grinding is performed until the thickness of the semiconductor wafer becomes not more than the depth of the grooves.
The groove depth measuring step preferably includes measurement of the full thickness of the semiconductor wafer before or after the groove cutting step, measurement of the remaining thickness of the semiconductor wafer at the groove after the groove cutting step, and calculation of the depth of the grooves by subtracting the remaining thickness from the full thickness. The measurement of the full thickness of the semiconductor wafer can be made advantageously by back pressure measuring means. The measurement of the remaining thickness of the semiconductor wafer at the groove can be made advantageously by laser light reflection measuring means. Preferably, a tape application step of applying a protective tape onto the face of the semiconductor wafer is incorporated after the groove cutting step and the groove depth measuring step.